6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 'J'] 



escapes from the test in the form of minute free swimming zoospores. 

 These where known are of about the size of the microspheric pro- 

 locuhim. From what is known of other groups of Protozoa, these 

 zoospores fuse, and the resulting cell becomes the proloculum of the 

 miscrospheric test. This is sexual reproduction. A true alternation 

 of generations is thus set up not unlike that found in other groups of 

 organisms. 



Before the two forms were known, " pairs " of species were de- 

 scribed, as in the case of the Nummulites where a large and small 

 species were often described from the same fossil horizon. These 

 are now known to be the microspheric and megalospheric forms of 

 the same species. 



HABITS 



A few species of the foraminifera live at the surface of the ocean 

 and are truly pelagic animals. Almost all of these are species of the 

 Family Globigerinidae. The test is modified by the addition of large 

 pores and large apertures allowing a free passage of the protoplasm 

 to the outside of the test. Most of the pelagic foraminifera tend to 

 assume a spherical form most completely accomplished in Orbulhia. 

 They occur in enormous numbers in such regions as the Gulf Stream, 

 and their empty tests form a very large proportion of the Globigerina- 

 ooze which makes up much of the ocean bottom. 



Most foraminifera are bottom-living forms, crawling about on the 

 ocean mud or attached to various objects on the ocean bottom. Their 

 motion is very slow. The most rapid rate I have timed at the 

 Tortugas was in Iridia diaphana Heron-Allen and Earland, which 

 travelled at the rate of about i centimeter in an hour. As various 

 species must crawl about considerably over the bottom in selecting 

 material for the test, this rate may be slower than the average. 



For the most part the food of the foraminifera consists of vegetable 

 matter, minute algae, etc., with occasionally some of the smaller 

 animal forms, such as copepods, which may be caught in the 

 pseudopodia. 



From observations made at the Tortugas, different species have 

 a repellant reaction when they touch one another. From certain 

 specimens it seems that the animal may leave the test at times and 

 either secrete or gather together material for a new and larger test. 

 From the life history and this last mentioned fact, it will be seen 

 that many of the tests of foraminifera are really empty and abandoned 

 tests of full grown individuals. This tends to make an unusual uni- 

 formity in the tests in spite of much of the supposed variation. 



